The present invention relates to an optically linked data processing system, and more particularly, to a coupler module for coupling optical transmission lines and a plurality of stations in such a system.
Fiber-optic transmission of data offers many advantages over the conventional forms of data transmission in data processing systems. Optical signals are generally immune to errors caused by electromagnetic interference (EMI) and radio frequency interference (RFI), and do not spark or short circuit. Furthermore, fiber-optic transmissions eliminate ground loop problems by providing electrical isolation between optically linked equipment.
In a distributed processing system, it is frequently necessary for plural processing stations to communicate with each other, as well as with peripheral equipment. A distributed processing system does not rely on a large central processing station to control all the operations performed within the system. Rather, many of the stations within the system perform their own processing, and when the processing requirements exceed the capability of any one station, another processing station assists.
Several considerations are often encountered in the design of optically linked processing systems. One is speed, and in copending U.S. application Ser. No. 939,727, entitled "Bidirectional Optical Coupler for a Data Processing System", by Amar J. Singh, filed Sept. 5, 1978, there is provided an optically linked system wherein two stations may communicate with each other simultaneously, rather than one station waiting until it receives the end of a transmission and the bus is clear before it can reply.
A second consideration in designing optically linked data processing systems, and particularly a distributed processing system, is that provisions be made for assuring the validity of signals carried over the transmission lines. For example, if two stations should accidentally transmit signals simultaneously, the resulting signal would be invalid and could not carry useful information to any other stations. Signal validity can be assured by having one station receive and record every signal and then replay or retransmit the signal so that the original transmitting station can compare or evaluate the retransmitted signal for accuracy. However, the time taken by a station to receive and then retransmit every signal obviously decreases the total operating speed and efficiency of the system.